Organic Geochemistry

by Irving A. Breger

Excerpt

The 5 major constituents of carbonaceous substances are carbon, hydrogen, oxygen, nitrogen, and sulfur. These elements are all Of low atomic weight and are thought to be products of low-temperature stellar reactions. They are widely distributed through the cosmos and play major roles in the thermonuclear processes of the stars. ~moreover, such isotopes as 6c, 8c1, 16832 and 16836 have total proton and neutron numbers divisible by 4 and are particularly abundant.

Carbon, hydrogen, and a number of other elements normally associated with carbonaceous substances have been detected in interstellar space, nebulae, stars, planetary atmospheres, and comets. Table 1 contains a summary Of abundances Of the first 28 elements of the periodic table as they occur in typical cosmic settings.

It is obvious from Table 1 that meteorites have lost a very high propor tion of their lighter elements, presumably through escape because Of low gravitational fields. The losses of hydrogen, because of marked volatility of its simpler compounds, and of nitrogen, because of its relatively low chemical affinity, are particularly important with respect to carbonaceous substances.

The tremendous abundances of the elements making up carbonaceous substances, C, H, N, O, and S, in most stars, and in the universe in general, direct one's attention toward their origin and distribution.